The present invention concerns a digital copying machine adapted to apply color separation to an image of an original, and to apply digital signal processing and reproducing the image.
Various types of so-called digital color copying machines capable of reproducing color original documents have been proposed so far. The digital color copying machines of this kind include those having recording means (image preparing station) for 4 colors (for example, cyan C, magenta M, yellow Y, Black BK; or red R, green G, blue B and black BK) and those having recording means for 3 colors (for example, cyan C, magenta M, yellow Y; or red R, green G and blue B).
In the copying machine having 4-color recording means, toner consumption and fixing energy are reduced by applying UCR (under-color-removal) and BP (black printing) thereby replacing the common amount of C, M and Y with BK toners. There are other types of copying machines in which signals for respective colors obtained from an original are supplied to corresponding color recording means at different delay times respectively and a color copy is obtained by a one-way path of recording paper.
While, on the other hand, those copying machines having 3-color recording means have a merit of causing less reduction in the saturation since UCR or BP processing described above is not conducted.
In any of the color copying machines described above, a single color or 2-color copy mode is of course possible in addition to the full color copy mode.
It is possible to add a 3-color mode function to those copying machines having 4-color recording means described above and select a 4-color copy mode and a 3-color copy mode. However, in those copying machines adapted to select the 4-color copy mode and the 3-color copy mode, there is no difference in the copy producing speed and, thus, in the efficiency of the copying work.
In addition, there are those systems of providing one page memory (so colled frame memory) for storing signals for a plurality of colors but they have a problem in that the copy producing speed is reduced when only one sheet of copy is prepared from one sheet of original, although it is advantageous to prepare a plurality of copies from one sheet of original.
Heretofore, in the case of preparing a kind (a sheet) of synthesis copy print from two kinds (two sheets) of original, printing is at first conducted to a first original, which is then placed in an intermediate tray and the printed copy is sent again from the tray to the recording station, where printing is conducted from a second original.
For preparing a plurality of (N) sheets of synthesis copies by such a copying machine, it requires procedures of conducting print cycles for N times with the first original, placing the printed copies in the intermediate tray and then applying printing cycles for N tymes on one identical transfer paper. Accordingly, there is a drawback that a copying time twice as long as the usual case is required in the synthesis mode.
In the conventional copying machine for preparing a mirror image copy from an image of an original, scanning with an original reading means is made in the direction opposite to the ordinary scanning direction (positive image copy). In a case where the scanning direction of such an original reading means is made switchable, the structure of the control system becomes extremely complicated for correctly controlling the position of the original reading means and mechanical control for the speed.
Furthermore, if the size of an original is smaller than that of a platen, there is a method of setting the original at the same position as that for the positive image copy and a method of setting it on the opposite side of the positive image copy. Although the former case can provide desirable workability to an operator, detection means for the original length has to be disposed for detecting the scanning start position. On the other hand, the latter has a drawback that the operator tends to cause error in setting the original.
By the way, it may at some time be required, in the copying operation, for a printed copy in which images on the left and right are exchanged with each other with respect to an optional position in the sub-scanning direction.
In a conventional copying machine, complicated procedures are necessary, for example, for conducting copying by placing an original on a platen such that one-half of the original is closed and the other half of the original is reproduced on a copy sheet, and then placing the original on the platen while closing the other remaining half of the original such that one-half of the original is reproduced on the copy.
It may be considered possible to constitute a digital copying machine of a type having one page memory (so-called frame memory) such that a left-to-right exchange copy can be prepared as described above. However, addition of the frame memory to a digital color copying machine having four image preparing stations with the aim of left-to-right exchange of an original image brings about a problem such as remarkable increases in cost.
A copy machine having a function such as preparing a symmetrical copy with respect to the sub-scanning direction has not yet been proposed. It may be considered that a digital copying machine or digital color copying machine having one page memory (so-called frame memory) can be constituted so as to obtain such a symmetric copy. However, addition of a frame memory for the exclusive use of a symmetric copy to a 4-full color digital copying machine having four image preparation station (recording means) provides a remarkable defect that the cost is increased significantly.
In any of the color copying machines described above, a single color or 2-color copy mode is of course possible in addition to the full color copy mode.
By the way, in the reproducing operation using a copying machine, there is an increasing demand for various forms of copies and one example of such requirement is the preparation of a copy in which a plurality of images from one original are disposed side by side on one identical transfer paper (hereinafter simply referred to as a multi-image copy).
It may be considered that such a multi-image copy may be prepared, for example, by recycling transfer paper as a recording medium by a required number of images, and preparing images while successively shifting the phase between the transfer paper and the original while simultaneously scanning the original for a number of times corresponding to the recycling times of the transfer paper. However, this method has the drawback that the copy producing time is considerably increased.
While, on the other hand, it is also possible to constitute that such image signals from an original are stored in a frame memory and the image signals are supplied from the frame memory to the image preparing station (recording means) for a plurality of times thereby preparing a multi-image copy. However, additional disposition of a frame memory for a multi-image copy to a full color copying machine having a plurality of image preparing stations and having a delay means to each of a plurality of image preparing stations has the drawback of remarkably increasing the cost of the reproducing machine.